Crystal Research and Technology最新文献

[Hanen Alhussain, Hela Ferjani, Youssef Ben Smida; https://doi.org/10.1002/crat.202300340]

[An error in the spelling of an author's name in the article. The name in the published paper is [Hanen] and should be corrected to [Hanan].

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Morphology-controlled Cs₂SbBr₆ crystals are synthesized by Bi- and Ag-substitution of the precursor solution. X-ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs₂BBr₆ (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs₂SbBr₆ is also confirmed by energy dispersive X-ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs₂SbBr₆ crystals with structural defects and multiphase formation.

Pristine tin selenide (SnSe) and copper (Cu) doped SnSe single crystals are grown by direct vapour transport technique. The energy dispersive X-ray, X-ray diffraction and Raman spectroscopic analysis of grown crystals show preferred stoichiometry having a single phase othorhombic SnSe. The electrical conductivity of SnSe and Cu doped SnSe are 24.24 and 106.06 S m⁻¹ at 310 K respectively which increase as temperature increases. Carrier concentration of grown single crystals are evaluated by the Hall effect. Lattice thermal conductivity of pristine SnSe is 0.61 W mK⁻¹, that decreased by copper doping to 0.44 W mK⁻¹ at 310 K and for both the crystals it shows decrement as temperature increases to 483 K. Seebeck coefficient of the grown SnSe and Cu doped SnSe are positive and obtained values are 536.44 and 492.90 µV K⁻¹ respectively at 310 K that confirm the p-type semiconducting nature. Power factor, Figure of merit and thermoelectric compatibility factor of grown pristine SnSe is 0.25 × 10⁸ µV mK⁻², 0.005 and 0.02 Volt⁻¹ respectively and shows improvement in Cu doped SnSe, i.e., 0.08 × 10⁸ µV mK⁻², 0.017 and 0.07 Volt⁻¹ respectively at 310 K. This shows Cu doping in SnSe makes it an effective thermoelectric device contender.

In this study, the propagation of plane waves in the lanthanum gallium tantalate (langatate, LGT) single crystals is investigated. Moreover, the flight time of different waves in the LGT rectangular parallelepiped sample is measured using the ultrasonic pulse-echo (UPE) technique, and the elastic constants of the LGT sample are determined. The experimental results clearly show echoes corresponding to the longitudinal and transverse waves along the x-axis. The waves along the z-axis have a similar property. However, the waves along the y-axis are more complex than those along the x- and z-axes. The echoes corresponding to the quasi-longitudinal waves along the y-axis are clear, but those corresponding to the transverse and quasi-transverse waves along the y-axis are not. The elastic constant can be accurately determined if the wave echoes corresponding to this constant propagate without distinct distortion and are clear; otherwise, it may be impossible to accurately determine the constant using UPE. All elastic constants $�c_{�i�j�}^E$ except $�c_{13}^E$ of the LGT single crystals can be determined using UPE from one sample. This study uses UPE to provide a reference for the characterization of elastic constants of piezoelectric crystals with 32 symmetry from one sample.

In this paper, it is found that taking a semitransparent melt, influences c–m interface shape, heat transfer, melt flow and von Mises thermal stress distributions, therefore the quality of the grown crystal. As a result, when absorption coefficients of both melt and crystal change from transparent to opaque case, the c–m interface convexity reduces from 12.5 to 5.8 mm, its shape becomes more convex toward the melt, and the maximum von Mises thermal stresses decreases from 69.55 to 13.8 MPa. For the second study, where the crystal absorption coefficient is fixed at $��20��m^{�-�1�}�$, the c–m interface convexity increases with the increase in melt absorption coefficient. The maximum and minimum von Mises stresses for the case $��100��m^{�-�1�}�$ are low compared to other values; then the grown crystal has a good quality.

A series of copper hydroxyphosphate (Cu₂(OH)PO₄) microcrystals with different shapes, including straw sheaf-like microcrystals, microrods-assembled microflowers, four-edged arrow-like microcrystals, and four-pointed star-like dendrites, are prepared by a hydrothermal method in Na₂HPO₄-NaOH buffer solutions. The buffer solutions serve as both reactant and solvent. More importantly, the pH values of the alkaline buffer solutions significantly affect the morphologies of Cu₂(OH)PO₄ microcrystals. Four samples have absorption bands in the near-ultraviolet, visible, and near-infrared regions; furthermore, four Cu₂(OH)PO₄ microcrystals exhibit different band gap energies (3.06, 2.78, 2.68, and 2.39 eV) owing to their different structures. This strategy can be scaled up for the simple, green, and low-cost production of Cu₂(OH)PO₄ microcrystals.

A twin-crystal magnesium (Mg) model with 9 different symmetric tilt grain boundary (STGB) angles (20°–80°) with preset nanohole defects is established by atomsk and lammps software. The mechanical behavior of grain boundary (GB) angles on twin-crystal Mg with cavity defects and its cavity evolution are simulated by the molecular dynamics method with embedded atomic potential, and the plastic deformation mechanism is revealed. The results show that the yield stress decreases with the increase of the STGB Angle during the stretching process. When the GB Angle increases from 20° to 80°, the yield stress decreases from 2.28 to 1.42 Gpa. This is because the larger the STGB Angle is, the larger the Schmidt factor is, and the easier it is to start dislocation slip during the stretching process. On the other hand, the larger the Angle of STGB, the more the number of atomic voids at the interface, and the more the number of dislocation nucleation points. The larger the Angle of STGB, the lower the strength of twinning Mg but the better the plasticity to avoid fracture. The plastic deformation mechanism mainly includes the nucleation of Shockley incomplete dislocation at STGBs, dislocation slip generates stacking faults (SFs), GB migration, and base plane dislocations.

The beneficiation of low-grade phosphate ore leads to the production of a substantial quantity of phosphate tailings, thereby not only occupying land but also endangering the environment and potentially posing safety concerns. In this work, extrusion molding, steam-curing, and calcined phosphate tailings are employed to fabricate lightweight wall materials with superior strength. It is found that the wall material has a special structure of interwoven needle-like crystals as a way to provide high flexural strength. The main composition of 34.94% phosphate tailings, 36.75% calcined phosphate tailings, 16.64% silica fume, 6.67% anhydrous magnesium sulfate is required to achieve an optimal maintenance process for 4 h of heat preservation at 120 °C saturated vapor pressure environment. The prepared wall materials yield a flexural strength of 24.9 MPa, compressive strength of 18.9 MPa, softening coefficient of 0.81, apparent density of 1.594 g cm⁻³, and thermal conductivity of 0.269 w/(m K), which meet the requirements of the Chinese standard “Lightweight strip board for building partition walls”. Moreover, the calculation revealed that phosphate tailings have a comprehensive utilization rate of 77.23%, effectively mitigating the issues arising from their accumulation and serving as an efficient means of utilizing solid waste derived from phosphate tailings.

The interfacial bonding state between each oxide and the silver matrix in AgCuOIn₂O₃SnO₂ electrical contact materials remains unclear. To address this, first-principles calculations using density-functional theory are employed to establish the low-index surfaces of Ag and SnO₂ and perform convergence tests. Computational results reveal that the Ag (111) surface and the SnO₂(110)-O surface exhibit the highest stability among their respective low-index surfaces. Consequently, these surfaces are chosen to form the interfacial model, and their atomic structure, adhesion work, and interfacial energies are systematically analyzed. The results demonstrate that the stability and interfacial bonding strength of the Ag(111)/SnO₂(110)-O interface are high, exhibiting metallic properties and strong conductivity. Moreover, at an interface spacing of d₀ = 2.4 Å, the interface stability is optimal. The redistribution of charge at the interface induces significant changes in the local atomic density of states, particularly noticeable in the Ag and O atoms. Additionally, the Ag/SnO₂ interface is predominantly bonded through ionic interactions, contributing to its robust bonding.